Friction coupling



Sept. 14, 1937. A. KREUSER 'FRIGTION COUPLING Filed Oct. 19, 1933 5 Sheets-Sheet l Inventor 4004 F KEEUSfQ/flM/N/STf/I me f/ W s. M J

Attorney- Sept. .14, 1937. A. KREUSER 2,093,281

FRICTION COUPLING Filed Oct. 19, 1933 5 Sheets-Sheet 2 fig-5 Inventor 4001 f/kfusfe, fifCfASEfi Attorney.

Sept. 14, 1937. A KRE SEF; 2,093,281

FRICTION COUPLING Sept. 14,1937.

A. KRE IUSER FRICTION COUPLING Filed Oct; 19, 1933 5 Sheets-Sheet. 4

- Attorney.

Sept. 14, 1937. A, KRE SER 2,093,281-

FRICTION COUPLING Filed Ocii. 19, 1933 5 Sheets-Sheet 5 iliillllllllllllllll/I Inventor 400A f/ffifujfe, 05(54550 A tto rney.

Patented Sept. 1-4, 19;.57

PATENT OFFICE FRICTION courLme Adolf Kreuser, deceased, late of Hamm, Westphalia, Germany, by Adolf Kreuser, Hamm, Westphalia, Germany, administrator- Application October 19, 1933, Serial No. 694,354

In Germany October 19, 1932 8 Claims.

The invention relates to friction couplings of the type comprising a hollow couplingmember which is expanded by a pressure medium (such as water or oil under pressure, compressed air,

steam or the like), and is thus pressed so firmly against a second coupling member that movement can be imparted by one coupling member to the other.

According to the invention the expansible wall of the hollow member which acts as the friction surface is formed as a metal tube the axis of which-coincides with the axis of the coupling the ends of which are integral with or rigidly secured in a fluid-tight manner to the inner or outer coupling member to which the tube is related and the metal tube is of such dimensions that the friction surfaces of the two coupling members may operate as bearing surfaces during free running. The invention also relates to the particular construction of the friction surfaces, that is to say thosesurfaces which are brought into intimate contact with each other by the expanding of the hollow member. Furthermore the invention relates to particular applications of the coupling.

The accompanying drawings illustrate by way of example several constructions and applications of the friction coupling according to the inven-' tion.

Figure 1 shows, in full section, a coupling for connecting together two shafts.

Figure 2 shows, in full section, a clutch for connecting a shaft to a gear wheel.

Figure 3 shows, in full' section, a form of coupling for connecting a shaft to a belt pulley, the

coupling being disposed to one side of the pulley.-

Figure 4 shows, in full section, a reversing gear with two couplings, the driven shaft rotating in one or other direction by engaging one or other of the left and right-hand couplings.

Figure5 shows, in full section, a coupling according to the invention on an enlarged scale.

Figure 6 shows, in full section, a modification of the coupling shown in Figure 5.

Figure '7 is a cross-section of a member partly filling a chamber for a pressure medium.

section of a coupling in which the frictional engagement is eifected by means of a hollow memberin this case carried by the shaft-which is expanded by the introduction of a pressure medium.

Figure 17 is a longitudinal section through a coupling sleeve which illustrates one particular construction of the friction surface.

Figure 18 is a detail side elevation of the inner surface of the bush adapted to fit the outer member of the coupling shown in Figure 16; 10

Figure 19 is a cross-sectional view showing the film of lubricant on an.enlarged scale.

Referring to the drawings:

In Figure 1, l is the power driven shaft havin the clutch core 2 made of metal such as steel; the shaft is mounted in the bearings 3. 4 is the shaft that is to be driven by engagement of the clutch; this shaft 4 is provided with the clutch sleeve 5 which is made of metal and is mounted in the bearings 6. The clutch sleeve 5 of robust construction is provided with an annular chamber 1 of which the tubular wall 8 separating it from the clutch core 2 is relatively thin. A bored out channel 9 extends advantageously'from the centre'of the shaft 4 to the annular chamber 1. If a pressure medium such as oil under pressure be passed through the channel 9 into the chamber 1, the thin wall 8 is expanded; this reduces the size of the interstitial space l0 which is finally eliminated abreast of the wall 8. The sleeve friction surface of the shaft 4 to be driven is thus pressed firmly upon the surface of the clutch core 2 of. the power driven shaft l and thus the clutch is caused toengage. If the pressure is released through the channel 9, frctional engagement between the friction surfaces is released. The interstitial-space I0 is restored as the stress to which the wall 8 is subjected lies beneath the elastic limit of the metal of which it is made.

I Whereas, Figure 1 represents a construction in which the-annular chamber to be placed under pressure lies in the clutch sleeve 5, Figures 2, 3, 4 and '5 show examples in which the annular chamber is in the clutch core 2. In Figure 2 --the toothed wheel I l runs with its fixed bushing IS, with the shaft [2 stationary, directly. uponthe friction surface of the clutch core 13, formed with the annular chamber 18. The hub l4 of the toothed wheel II is in this case formed as a clutch sleeve of robust construction. The interstitial space I0 may lie within the limits usual in bearingsfthat is to say, it is about one-tenth to three-tenths of a millimetre wide-according to the diameter of the clutch core l3. A ring i6 is screwed or otherwise connected to the toothed 40 the same conical shape as the core 31.

wheel |.i and engages in a corresponding recess in the clutch core preventing axial movement of the toothed wheel I I. The pressure medium is introduced through the tubular channel H mm 5 the annular chamber ll between whose outer thin wall and the inner surface of the bushing it frictional engagement, is produced.

- The construction according to Figure 3 corresponds to that of Figure 2. In Figure 3 the clutch 1o sleeve It forms a separate part to which is secured the belt pulley 2. with the loosely mounted bush 2i which may be secured to the pulley.

In Ii'lgure 4. 22 is a driving shaft adapted to be connected through clutches 2t, 21 with either of two bevelled wheels 22 and 24 in mesh with a bevelled wheel 25 on the driven shaft. The clutch cores 24 and 21 have thin walls and 2s ontheir external peripheries. The pressure medium passes through the stationary tube 30 20 mounted in the hearing or stufling-box 3 I, thence through the channel 32 into the chamber 33, that is to say, into the clutch 21, while the clutch 20 is in similar manner supplied with the pressure medium through the channel 34. The

toothed wheel 2' makes right-hand or left-hand rotational movements according as the pressure medium is supplied to one or other of the clutches, ,the shaft 22 rotating in one direction only.

Figure 5-illustrates a clutch on an enlarged scale. The toothed wheel a normally runs loosely on the spindle 20 but is adapted to be clutched and is shown as being welded at the ends to the 35 hub 30 keyed to the shaft 3'. The clutch core 21 is slightly conical inshape on the friction surface. The clutch sleeve 39 which is secured to the toothed wheel I! by wedges or the like carries a bush 42, which is internally provided of The interstitial space ll may be set by moving the clutch sleeve 28 with the bush 4| axially by means,

for example, of a screw-threaded ring 4| adapted to be rotated to a limited degree in relation to 5 the sleeve 10 and the bolts by which it is held in position upon the annular hub cap secured to the wheel 35 so that it is quite easy to make the necesary adjustments having regard to the wear which sets in in due course. In the modified construction shown .in Figure 6, the ends of the clutch core 21 are thickened in the radial directioninwardly and are shrunk directly onto the hub 38. The hollow space 42, which for manufacturlng reasons is of a considerable size in the shrunk construction because the ends of the clutch core I! must be of very robust construction by reason of the shrinkage while the wall must be thin because it has to expand, must" in that construction be as nearly as possible filled with a filling member 42 as represented in detail in Figure 7 with a view to economize in the volume of pressure medium present, because of the compressibility of liquids. The member 43 is made in several parts to facilitate the mounting of it in position.

In practice the bored-out space 42 is always maintained full with pressure medium that is not under pressure. For the purpose of eiIecting the engagement of the clutch the pressure medium is put under stress by a pump or an electric thrust magnet or from a plant or the like supplying liquid under pressure. To release the clutch the pressure medium is released from pressure without the space 42 being emptied. The 1 pressure medium utilized every time the clutch is engaged is made up of the quantity of pres sure medium required for enlarging the hollow space 42 with a view to the elimination of the interstitial .space i0, and of that quantity of pressure medium which corresponds to the com- 5 pressibility of the pressure medium in the hollow space 42, which is not previously compressed. It is known that the compressibility of liquids.

v is inconsiderable in comparison with that of a gaseous medium but, nevertheless, a liquid is also 10 compressible. The consumption of energyin the engaging of the clutch is minimized by partially filling the space 42 with the filling member 43.

device.

The material from which the clutch core 31 is made is relatively hard, having a Brinell hardness of 300 to 370. The bush 4. is made of a 20 special bronze. For effecting the engagement of the clutch the pressure medium is allowed to enter the hollow space 42 of the clutch core through the channel 44. If the pressure of the pressure medium in the space 42 has reached 25 about 50 atmospheres the thin wall of the clutch core 31 has expanded or increased in diameter to such an extent that the play of 0.1 mm. in the case of small clutches, up to 0.3 mm. in very large clutches has disappeared, so that by press- 30 ing the clutch core against the bush 40 frictional engagement is effected. If the pressure of the pressure medium rises still further the thin wall of the clutch core 31 starts to press against the wall of the bush 4. and the shaft 36 is caused 35 to rotate. If, for exampg, the pressure in the hollow space 42 rises-to 200 atmospheres the. pressure between the friction surfaces rises to about 150 kg. per sq. cm. and if the pressure in the hollow space 42 rises to about 500 atmos- 0 pheres the pressure between the friction surfaces is 450 kg. per sq. cm. The conditions of operation are thus extremely favourable for the clutches. Wear is extremely small if the material is correctly selected and there is adequate lu- .45 brication. The load capacity is extremely great if it be considered that such a clutch can be driven perfectly with a .pressure of 500 atmospheres or over existing in the hollow space 42.

The frictional coefdcient in the case of an ex- 5 Y panded clutch 'core is, according to present knowledge, about 0.15, whereas the frictional coefficient for free running (liquid friction) is about 0.02. There cannot be on the thin wall any premature fatiguing of the metal from which the 5 the clutch core 21 is made has, however, an elastic limit of '75 kg. per sq. mm. On the other hand the wall is not so thick that the elastic limit cannot even then be exceeded if the clutch core were to be under the influence'of the high pressure 'of the pressure medium without the clutch 65 sleeve around the clutch core. Normally,'-llowever, the clutch core cannot be stressed to' any greater degree than corresponds to its distension of mm. and mm. respectively, because the still steel clutch sleeve 39 with the bush 40 pre"-. vents any distension beyond the amount indicated", and therefore also prevents any additional stressing.

The action of the clutch, put shortly, 'is a,

changein the conditions from a loose bearing to a tight joint or a shrunk-on joint on engagement or conversely on,disengagement. A consideration of the conditions indicates that by reason of the friction coeilicient which completely changes during close fit or during shrunk-on fltas compared with the loose flt the clutch of relatively small dimensions is suited to the transmission of large turning moments. An important improvement in the clutch is that, for example, in the to case of presses, shears, punches or the like the clutch can make partial thrusts and can be easily disengaged while under full load. It is therefore effective as a control clutch because, for example, where a machine or the like commences to b e l5 over-loaded the clutch can be instantaneously disengaged by a control actuated by the machine itself. It is a simple matter to construct the control so as to be able to engage and disengage the clutch rapidly or slowly according to the needs of the drive. As the clutch occupies little space, and can run totally immersed in oil and is not provided in the interior either with rods or packihgs, it is very suitable for use in precision apparatus. In one and the same clutch the clutch core as well as the clutch sleeve can be provided with'a hollow chamber and further examples of construction can be cited which do not depart from the scope of the invention. a

In the construction according toFigure 8 the hub 46 is keyed to the driving shaft 45. The clutch core 41 surrounds the hub 46 and'serves to produce frictional engagement with the toothed wheel which is to be driven, and is secured to the hub 46 by means of the shrunk-on ring 48, the purpose being first to transmit the movement of rotation and in addition to render unnecessary the use of special means'for maintaining a tight joint. The'left hand end of the clutch core 41 is provided with a flange-like shoulder 49 which in 40 turn is shrunk on the reduced end portion'of the hub 46 of the clutch. Between the hub 46 and the clutch core 41 a hollow space is formed into which the pressure medium (water or oil under pressure, compressed air or the like) is fed through the channel 5|. The reduced end portion of the.'hub 46 is provided with a' screwthreaded extension which serves the purpose hereinafter described. The bush 53, which encloses the slightly conical clutch core 41 is secured 50 in the clutch sleeve 52 and is of conical'shape to correspond to the conical form of the clutch core 41. The clutch core 41 which, as hereinbefore described, is fixed to the driving spindle 45 rotates, in the bush 53 which in turn is secured to the 55 clutch sleeve 52 upon which is mounted the toothed wheel 54. The adjustment of the bearing so constructed is effected by the flange 55,

which is in threaded engagement with the screwthread of an annular projection of the sleeve 52. The flange disc 55 is rotatably mounted in the groove formed between the flange-like shoulder 49 and a screw-threaded ring 56 engaging the screw-threaded extension of the hub 46. 'The flange disc 55, on being rotatably adjusted, moves shown, of the clamping ring 51 which is rotat ably seated on the flange disc 55. The clutch sleeve 52 is, however, moved axially with the bush 53. The key 58 which prevents rotary movement of the toothed wheel with respect to the clutch round with the core.

'ter.

shrinking into the clutch sleeve 68 is effected by I sleeve. After the adjustment has been satlsfactorily made the bolts of the clamping ring 51 are tightened tov secure the relatively rotatable parts together.

41 which is between the flange-like shoulder 49 and the shrunk-on ring 48 is expanded and is pressed against the bush 53 of the clutch sleeve 52, thepressure being so great that the clutch sleeve 52 and the toothed wheel 54 are carried When disengaging, the clutch core 41 regains its original condition. By means of this construction the clutch sleeve 52 with the corresponding toothed wheel 54 can be readily fitted in place and removed again.

According to Figure 9 the clutch core 59 at one end is shunk hot on the shaft 6| by the use of the shrunk-on ring 60. The left-hand end of the clutch core 59 is turned on its external periphery of slightly conical form and is forced tightly on tothe shoulder of the shaft 6| by means of the ring 62 which is bored out conically on the contacting surface to correspond to the form of the clutch core 59, and is secured by the Whereas in the constructions illustrated in' Figures 8 and 9 the expansible hollow member is provided on the shaft, in the constructions according to Figures 10 and 11 the hollow member is provided in the clutch sleeve.

According to Figure 10 in which the expansible clutch ring 66 is provided at one end with an external flange 61, this flange is shrunk by heat into the clutch sleeve 68 which is formed as a toothed wheel by heating the hub of the lat- On the other end of the clutch ring 66 the means of the ring 69. 16 is the space for the pressure medium which space is formed between the clutch core 66 and the clutch sleeve 68. The

stub end of the shaft H carries the bush 12 which is secured to it. In this construction the clutch sleeve 66'-with the ring 66 can be directly with the toothed wheel 14, which at the same time shrinkage. and on the other by cold shrinkage with the assistance of rings.

Figure 12 shows on an enlarged scale the carrying out of the cold shrinkage in the clutch according to Figure 11. In this connection the ring 15, which is turned of conical form on-its external face is driven into the end of the clutch ring I6 which is likewise conical, and is held in this position by the ring 11.

According to the Figure 13, which figure represents a modified construction of the clutch according to the invention, the clutch core 18 is secured at its ends to the shaft 19 by welding so as to form a tight joint, the shaft being turned acts as clutch sleeve, on the one hand'by hot of reduced diameter between the ends of the core .118 to: form the pressure space- According to Figure 14 the clutch core 88 is welded to the ,clutchsleeve .81; the pressure mediumcha rlberv 82 being formed in the clutch sleeve II which the example illustrated the connection between the ring 88* and the shaft is produced by welding.

In the clutches hereinbefore described it is frequently desirable, especially where the surfaces are lubricated, to shorten the time which is taken in the operation of engagement until the co-acting clutch members are completely in engagement. To effect this. the contacting surfaces of the clutch are divided up more or less in some manner or other, for example, in square, rhombic, circular or similar surfaces, by such means, as grooving. 'By the suitable arrangement and dimensions of these surfaces it is a simple matter to adapt the time taken for 'engagement to the needs of the case.. By this process itis possible without trouble to arrive at clutching periods which lie between 0.1 second and more than a minute. If, for example, the surfaces are made relatively small, during the operation of engagement, the lubricant has. to move through only small distances and the friction surfaces are thus brought rapidly into complete engagement By this means it is possible to cause the friction clutch to engage practically instantaneously.

The division of the friction surface-of the friction clutch according to the invention into distubular wall 88:: in the bush 82 the inner surface of which is grooved peripherally and transversely and which is secured to the clutch sleeve 8|. The sleeve 8| haslreyed to it the pinion 88 which serves for conveying away energy. Figures 17 and 18 illustrate the bush 8! the surface of which is divided by a system of peripheral lubricant channels 85 and longitudinal lubricant channels 88, into-separate rectangular surfaces, the channels being relatively deep.

.Fi'gure 19 show'son an enlarged scale the contin'uous film of lubricant 88 that is present in the free running condition of the clutch described,

. and it furtherillustrates the paths of flow. of the lubricant as far asthe lubricant channels.

One very useful application of the clutch hereinbefore described, having effects which cannot be obtained with the clutches already available is obtained in mechanically driven machines such, for example, as presses of every kind (forging presses, artificial resin presses, punching presses,

drawing presses and similar shears, stamps, and the like.

The friction clutches hereinbefore described have the advantage that they'are put into engagement without shock and can be engaged or disengaged while transmitting turning moments of any degree and put into and out of engagement under full working stress. With these properties\ I available it is possible by using the friction clutch according to the invention on machinery to combine the good qualities of a mechanical machine with the new properties of the clutch in an ideal manner.

Machines which are fitted with the known types of disengaging clutches have the following disadvantages:

I. If the machine known types of friction clutch, the clutch is mountedon the highspeed motor shaft or a relatively rapidly rotating counter-shaft as these known constructionsare not adapted to transmit very large or even large turning moments. To permit power to be transmitted, also, most machines are so constructed that large transmission wheels and gearing are n. The momentum .of these wheels is suflicient alone to isfittedwithoneofthe aflect the machine that is lmder load, when the clutch is disconnected. Thus it is obligatory in order to prevent such'disturbances to protect the machine by hydraulic in! other safety devices.

These elements have disadvantages such as untrol of the machine precisely because of the inertia of the intermediate gearing and the large masses, Exact control is, however, of the'greatest importance on most presses, stamps and the like.

11. Machines which are provided with other known engaging and clutches (such .as dog clutches, pin clutches. rotating wedge clutches and similar clutches which must, however, operate as a rigid connection during the actual operation of the machine) have the disadvantage thatit is not possible to engage the parts of the clutch in any position that may be desired because the driving member must first take up aparticular relative position with respect to the driven member to produce the clutch ing action. It is known that with suchclutches disengagement is not possible under load. 'If therefore when such clutches are in use oe is oifered which is greater than that allowable for the machine, the machine unquestionably may be damaged, provided that safety devices with their known disadvantages are not protecting the machine against such damage. control is impossible with this type of clutch as engager III. Electro-magnetic clutches, which in themselves to a certain extent meet-the demands made on an ideal clutch as regards being able to- Furthermore, they are unsatisfactory in that the.

magnetizing necessary for the engaging- Operation and the demagnetialng necessary for disengaging always take periods of about a" second. Apart from the fact that the must be provided paragraph numbered 1) the engaging-or disengaging time is one second, so that it is not pos- 5 sible to have complete .control of the machine especially necessary in time, of danger. If it be assumed for example that in the case of a press which is operating at the speed of 300 mm. per second, there is a sudden inadmissible high resistance developed the machine will have stopped or even have been damaged, long before the disengaging operation of the clutch is completed. Consequently the influence of the rotating masses and .their great kinetic energy is left out of consideration. The magnetic clutch, therefore, with respect to its special qualities,,by no.

' means satisfies the demands to be made upon an ideal clutch, and still renders necessary the use of the safety elements which have already been described but which to say the least are unsatisfactory in action.

IV. Starting with the knowledge of the inadequacy of the known types of clutch a partial change was made in the direction of fitting the machines with reversing motors without, however, in so doing finding the ideal control. This is quite-clear from the very fact that reversing motors need a starting-up time of at least one second and a stopping time of not less than half a second. The stopping time, however, even with very good reversing motors, the cost of which is extremely high, is such that breakdown of the machine is not impossible at moments of danger.

Practice shows that when reversing motors are employed it is not possible to operate without the use of safety devices, which usually are faulty in operation.

V. Purely hydraulic plants have excellent controlling .means provided but the enormous expense of the plant and thelow eiiiciency render their use uneconomical.

It will be seen from what has been stated in paragraphs I to III that mechanical presses already fitted with known engaging and disengaging clutches still have disadvantages the elimination of which has hitherto been impossible although this ishighly desirable in the interests of safety and of the plant.

The use of the friction clutch according to the invention with machines of a kinds particularly forging presses, metal ex sion presses, artiflcial resin presses, perforating presses, drawing presses, shears, stamps and the like, introduce advantages unobtainable with the known forms .of clutch. The clutch according to the invention is excellently suited, as experiments -have shown, for transmitting extremely large turning moments. The possibility is thus provided, as has been demonstrated by experiments, of applying the clutch to machinery and therefore of avoiding the considerable disadvantages set forth under paragraphs 1 to V and which are inevitablyinvolved in the application of a clutch to the motor shaft .or a high speed counter-shaft as regards its capacity for manipulation.

With regard to the capacity for control of the clutch hereinbefore described, a great number of experiments spread over many months have demonstrated that the clutch can be engaged and disengaged in every position practically instan taneously, and it has to be emphasized that the clutch can be disengaged under full load at any time perfectly and instantaneously. The clutch 75 engages under load perfectly andinstantaneously so that it is impossible for the gearingto be damaged. If the clutch be mounted on a slowly rotating shaft the machine can beoperated, having regard to the excellent properties of the clutch in a manner which has not been attainable by' means of the clutches hitherto employed. This does not take into consideration the fact that the undesirable influence of the rotating masses and their kinetic energy on the capacity for manipulation of the machines can be completely eliminated, by arranging the clutch on the slowly rotating working shaft.

A further advantage of the friction clutch according to the invention, hitherto not attained in so perfect a manner, is that the clutch automatically controls the turning moment which it transmits. 7

If the maximum turning moment, the amount of which can be exactly determined for each working operation that occurs, independently of the size ofthe clutch, by adjusting the pressure on the friction surfacesthat is to say by regulating the pressure of the pressure medium-is exceeded, the clutch commences to slip and the working operation is thus instantaneously interrupted. This renders it impossible from the outset for the machine or its parts to be broken. Consequently for the first time the responsibility for the safety of the machine against breakage by overloading is transferred to the clutch. The safety devices which hitherto have been operated by hydraulic, mechanical or other means can therefore be at once dispensed with by the use of the friction clutch according to the invention. This clutch does not therefore represent a clutch merely but it is at the same time an excellent safety element, a safety clutch, which once having functioned is immediately available again without any part being damaged and without the necessity of any part being changed. The clutch according to the invention differs from the safety clutches with shearing pins or the like which have-been hitherto used.

A further field of use for the friction clutch I according .to the invention is in connection with transmission gearing, namely reversing gearing, stepped gearing and combinations thereof. Such gearing is employed in rolling mills, rack-draw benches, crank presses, machine tools, and vehicles. The use of the clutch hereinbefore described in gearing of the kind described oflers such advantages over the use of clutches of other types that the machines produce entirely new effects. Reversing. gearing provided with known types of clutches takes up considerable space. For such gearing leaf spring clutches provided with friction clutches placed in front are much used because a leaf spring clutch by itself engages with a jerk. In change speed gearing electromagnetic clutchesare also employed for reversing, but in this case an electric supply has i to be relied upon.

Reversing gears provided with the friction clutch according to the invention can be constructed very easily and they occupy little space. With such gearing any desired turning moment can be transmitted and the actions of engaging anddisengaging can be effected without jolting and without the use ofintermediate elements.

Change gearing is at thepresent time constructed with sliding wheels or, when the turning moment is small, with simple friction clutches, whereas theknown typespf clutches incomparison with the wheels are of dimensions which at the present time are not admissible.

'pinions do not differ substantially from change gears with sliding wheels. For this reason the construction is exceedingly compact. All the wheels are in'permanent engagement and it is possible to change from one speed to another without jolting. It is now also possible to con- Y struct stepped gearing which has such advantages over the known stepped gearing that machines having entirely new effects can be built.

What is claimed is:

1. A friction clutch comprising a clutch member with a rigid clutclsurface and a hollow clutch member concentric therewith, the said hollow clutch member' being bounded on the side acUacent the rigid clutch surface by a clutch surface formed by a tubular expansible wall of metal, the axis .of which wall is coincident with the axis of the clutch and the ends of which are rigid and fast to the hollow clutch member to provide a fluid-tight closure to the hollow chamber of the said clutch member, in which a pressure medium is caused to act to expand the metal wall into flrm contact with the rigid clutch surface.

2. A friction clutch according to claim 1, characterized in that the tubular wall is of a form such that it may be shrunk into position with respect to the hollow clutch member.

3. A friction clutch according to claim 1, wherein the friction surfaces of the; clutch' members are conical by reference to the clutch axis and the clutch members are free to move relatively in the axial direction and adjusting means are provided whereby relative axial movement of the clutch clutch surface.

members is effected for variation of width of the interstitial space.

4. A friction clutch accordingto'clalm l, char-.

acterized inthat filling member's partly inf the hollow chamber of the hollow clutch member.

5. A friction clutch according to claim 1, chara'cterized in that the tubular wall of the hollow clutch member is of increased'thickness at least at one end.

6. A friction clutch according to claim l, characterized in that the tubular wall of the hollow clutch member is of a form such that it may be closed by a tubular expansible and integral metal wall forming the clutch surface, to said clutch surfaces of the two clutch members operating as bearing surfaces when the clutch'isnot operated, and means for the application of a pressure medium within the hollow chamber of the hollow clutch member for the expansion of the expansible wall into frictional engagement with the rigid ADOLF' KREUSER. Administrator 0 the Estate of Adolfi Kreueer, Deceased. 

